The present invention relates to a genetically-engineered Mycobacterium strain and a use thereof in the preparation of steroidal compounds. The genetically-engineered Mycobacterium strain is a Mycobacteria which lacks of acyl-CoA dehydrogenase genes fadE31, fadE32 and fadE33, wherein acyl-CoA dehydrogenase genes fadE31, fadE32 and fadE33 respectively encode proteins as follows: having amino acid sequences according to SEQ ID NOs 4, 6 and 8; derived by substituting, deleting or inserting one or more amino acids in the amino acid sequence defined by preceding protein and having the same function as that of the preceding protein. The present invention constructs a genetically-engineered Mycobacterium strain and applies it in preparing steroidal compounds, thereby enriching the types of valuable intermediates, improving the production efficiency and product quality of steroid drugs, reducing energy consumption in the steroid drugs production, simplifying production steps, and reducing production costs.

Disclosed herein are method of detecting the presence of living cells in a sample by detecting the death of those cells. Because cell death can occur more rapidly than cell growth, which is often the parameter used to detect living cells, detection by death can reduce the time to detect certain organisms. Further, the present methods can distinguish between the presence of dead cells which may leave traces of, for example, detectable genetic material, and living cells that are of concern in situations such as diagnosing an infection.

The present invention relates to a genetically-engineered Mycobacterium strain and a use thereof in the preparation of steroidal compounds. The genetically-engineered Mycobacterium strain is a Mycobacteria which lacks of acyl-CoA dehydrogenase genes fadE31, fadE32 and fadE33, wherein acyl-CoA dehydrogenase genes fadE31, fadE32 and fadE33 respectively encode proteins as follows: having amino acid sequences according to SEQ ID NOs 4, 6 and 8; derived by substituting, deleting or inserting one or more amino acids in the amino acid sequence defined by preceding protein and having the same function as that of the preceding protein. The present invention constructs a genetically-engineered Mycobacterium strain and applies it in preparing steroidal compounds, thereby enriching the types of valuable intermediates, improving the production efficiency and product quality of steroid drugs, reducing energy consumption in the steroid drugs production, simplifying production steps, and reducing production costs.